This invention relates to motor vehicle brake systems, and more particularly to a method of using measured brake pedal position and vehicle deceleration to diagnose brake system abnormalities.
The effectiveness of a vehicle braking system can change dramatically over time due to brake wear, fading and poor adjustment, and system abnormalities such as hydraulic leaks and air in the brake lines. Since the changes in braking effectiveness may go unnoticed by the driver, some sort of diagnostic logic is desired to inform the driver that a repair or adjustment of the braking system is needed.
The present invention is directed to an improved method of diagnosing conditions of a vehicle braking system that degrade the braking effectiveness, and informing the driver of the condition so that repair or adjustment can be timely made. According to the invention, the relationship between brake pedal position and vehicle deceleration is determined during a calibration interval to construct a calibration table of braking effectiveness, and then periodically over the life of the braking system to develop a current braking effectiveness table. Braking system abnormalities that impair the braking effectiveness are diagnosed by analyzing the table values. In the illustrated embodiment, non-adjusted rear brakes are detected by comparing a front-to-rear wheel speed difference with a pedal position dependent threshold, leaking brake fluid and brake fading are detected by comparing an actual vehicle deceleration with a vehicle deceleration expected based on the calibration table, and brake wear is detected by comparing current table values with calibration table values.